Wide-band high-power delay line

ABSTRACT

In a delay line of an electron tube for amplifying or generating microwaves, externally of and parallel to a main conductor helix within which an electron beam travels axially, there extends a secondary helix which has a pitch and a diameter half the size of those of the main helix and which is so arranged that its turns electrically contact those of the main helix at several locations along a generatrix common to both helices. The field effect generated by the secondary helix substantially diminishes parasitic phenomena that appear in a delay line having a main helix of large diameter.

United States Patent Kantorowicz 1451 May 30, 1972 [54] WIDE-BAND HIGH-POWER DELAY LINE [72] Inventor: Gerard Kantorowicz, Paris, France 73] Assignee: Thornson-CSF I [22] Filed: Dec. 16, 1970 [21] Appl.No.: 98,615

[30] Foreign Application Priority Data Dec. 16, 1969 France ..69435l0 52 U.S. c1 ..'.....31s/3.s, 3l5/3.6 511 im. c1. H01] 25/34 [58] Field olSearch ..3 15/16, 3.5 x, 39.3 x, 3.5, 315/393 [56] I References Cited 1 UNITED STATES PATENTS 2,971,114 2/1961 Dow .Q. ..3l5/3.6 2,834,908 5/1958 Kompfner ..3l5/3.6

2,824,257 Branch, Jr. ..315/3.6 2,707,759 5/1955 Pierce ...315/3.6 2,887,609 5/1959 Dodds... ...3 1513.6 3,054,017 9/1962 Putz ...315/3.6 3,427,495 2/1969 Famey ..3 l 5/3.6 X 2,823,333 2/1958 Quate ..315/3.6

Primary Examiner-Eli Lieberman Assistant Examiner-Saxfield Chatrnon, Jr. Attorney-Edwin E. Greigg [57] ABSTRACT In a delay line of an electron tube for amplifying or generatingmicrowaves, externally of and parallel to a main conductor helix within which an electron beam travels axially, there extends a secondary helix which has a pitch and a diameter half the size of those of the main helix and which is so arranged that its turns electrically contact those of the main helix at several locations along a generatrix common to both helices. The field effect generated by the secondary helix substantially diminishes parasitic phenomena that appear in a delay line having a main helix of large diameter.

' 7 Claim, 7 Drawing Figures Patented May 30, 1972 3,666,984

2 Sheets-Sheet 1 2 i p/Z Patented May 30, 1972 2 Sheets-Sheet 2 BACKGROUND OF THE INVENTION This invention relates to electron tubes for generating or amplifying microwaves. Frequently, for this purpose, electrical conductors are used which are helically and cylindrically wound and which have equidistant turns.

The propagation of an electromagnetic wave along such a structure induces an electric current in the conductor and develops in the space delimited by the helical cylinder a system of electric and magnetic fields, the displacement of which along the axis of the helix is associated with that of the electric current. It is known that under these circumstances the helix acts as a delay line with respect to the system of fields whose speed of displacement bears the same relation to the speed of the current as the ratio of the helix pitch to the length of one turn. Such a reduction in the speed of the fields is necessary for bringing the speed to the same order of magnitude as that of the electrons of the electron beam which is normally injected along the axis of the helix and to thus permit said electrons to interact with the electric field of the wave.

By increasing the diameter of the helix, the power of such electron tubes may be increased, since the input electron beam may be more powerful. In case, however, the diameter of the helix exceeds the wavelength in the order of 1/10, higher modes or space haromonics appear in the wave propagation. These constitute a significant, nonutilizable portion of the output power.

Moreover, some of these harmonics are propagated in the so-called inverted mode and may interact with the electron beam, causing a self-oscillation. of the electron tube. This phenomenon thus constitutes a limitation upon the helix diameter.

In addition, since the electric field associated with these inverted space harmonics" is located substantially adjacent the helix, in order to avoid undesired interaction, the electron beam should have a small diameter compared with that of the helix. This requirement thus places a limitation on the diameter of the electron beam.

The known solutions proposedfor boosting the power, such as using double helices with reversed pitches, or periodically charging the helices, lead to a restriction in bandwidth.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the invention to provide an improved delay line of the aforenoted type which, without affecting the known characteristics of wide-band propagation by means of a simple helix, permits its use for substantially higher power.

Briefly stated, according to the invention, there is provided a delay line for a microwave electron tube which has a main helix formed of a cylindrically wound electric conductor and a secondary helix, also formed of an electric conductor and wound in the same direction as the main helix; the secondary helix is dimensioned in such a manner that the ratio of the main helix diameter to the secondary helix diameter and the ratio of the main helix pitch to the secondary helix pitch are identical integers greater than 1. Further, the secondary helix is disposed externally of and parallel with the main helix in such a manner that those of their turns which are located opposite one another are in electrical contact along a generatrix common to both helices.

The invention will be better understood as well as further objects and advantages will become more apparent from the ensuing detailed specification of two exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic side elevational view of a first embodiment of the invention;

FIG. 2 is a schematic side elevational view of a second embodiment of the invention;

FIG. 3 is a schematic side elevational view of a microwave electronic tube comprising a helix assembly as shown in FIG. 1;

FIG. 3a is a sectional view along line Illa-Illa of FIG. 3, and

FIGS. 3b, 3c, 3d are cross-sectional views similar to FIG. 3a and showing an arrangement of secondary helices when the number of the latter is two, three, or four, respectively.

DESCRIPTION OF THE EMBODIMENTS Turning now to the embodiment illustrated in FIG. 1, there is shown a main helix 1 having a pitch p and diameter D, and an associated secondary helix 2 which is wound in the same direction as helix 1 and which has a pitch p/2 and a diameter D/2. An electron beam 11 passes axially inside the main helix 1.

Helix 2 extends externally of and parallel with helix 1 and is in contact therewith at locations 3, 4 and 5.

In operation, the electric current induced by the microwave in the main helix 1, also flows in the secondary helix 2 by virtue of said points of contact. The axial electric fields as sociated with the two helices travel at the same speed since the delay factors of the two helices are identical. This is so because the ratios between the diameter and the pitch in each helix are the same, and, as set forth before, the delay factor is a function of said ratio.

The magnetic fields associated with these electric fields have a general distribution such that their lines of force surround the wire conductor in which the currents flow. Thus, for example, the lines 7 and 8 are associated with the main helix 1 and the lines 9 and 10 pertain to the secondary helix 2. The respective directions of the magnetic field lines are indicated by the arrow heads.

In the zones of contact, where the two helices are tangential to one another at a generatrix, the magnetic field prevailing in the main helix 1 adjacent the wire conductor results from the addition of the internal field of main helix 1 and the external field of the secondary helix 2. These magnetic fields, however, are of opposite direction; they thus oppose one another inside and in the vicinity of the conductor forming the main helix. Consequently, the corresponding magnetic energy will be less than in the case where the main helix is considered alone.

It is well known from the theory of electromagnetic fields that the electromagnetic field existing inside a helix may be resolved into a part known as the transverse electric field, whose magnitude is associated with the longitudinal magnetic component, and into a part known as the transverse magnetic field whose magnitude is associated with the effective longitudinal electric component. For a single helix, the total energy is substantially equally divided between each of these two field portions. Then the function of the secondary helix may be interpreted as follows: The presence of the secondary helix reduces the portion of magnetic energy in the fundamental component and consequently increases the magnetic energy in the other space harmonics; the electric energy associated with these harmonics is essentially of the transverse electric type which does not interact with the electron beam. The result is a reduction in the longitudinal electric field of the harmonies and therefore, in particular, of the inverted space harmonic which generates parasitic oscillations. It is to be understood that the foregoing interpretation in no way limits the scope of the invention.

Thus, in an electron tube having a helix assembly in accordance with the invention, the diameter of helix 1 may be increased without any risk of decrease in output, and further, the diameter of the injected electron beam 11 may be of similar magnitude without any risk of introducing self-oscillation. In this manner high-power wide-band tubes may be obtained.

FIG. 2 illustrates a second embodiment of the invention where two secondary helices 2 and 12 both dimensioned as described in connection with the secondary helix 2 of FIG. 1, are disposed parallel to the main helix 1 contacting the latter at two generatrices located along diametrically opposed sides of helix 1. In such an arrangement the plane containing the axes of the three helices constitutes the plane of symmetry of the electric fields.

FIG. 3 shows a microwave electron tube wherein an electronic gun 21, which produces an electron beam (not shown), and a collector of electrons 22 are disposed in the axis of a main helix 1. The electron beam travels along the axis of the main helix which further bears at least one secondary helix 2, as shown in FIG. 1, the main helix being conventionally connected with an input terminal 23 and an output terminal 24. The respective disposition of main helix 1 and auxiliary helix 2 is further illustrated in cross-seetional FIG. 3a.

FIGS. 3b, 3c, 3d are transverse sectional views of a microwave electron tube in which there are provided two or more secondary helices 2, which are evenly distributed about the periphery of the main helix 1. Such a disposition enables a reduction of the resistance coupling on the undesirable propagation mode, whereby more output power can be obtained.

What is claimed is:

1. in an electron tube delay line for a microwave electronic tube, the improvement comprising A. a single main helix wound cylindrically with an even pitch and adapted to be traversed internally and axially by an electron beam and B. at least one secondary conductor helix wound cylindrically with an even pitch in the same direction as said single main helix and extending externally thereof and parallel thereto; said single main helix and said secondary helix being in electric contact with one another at several locations along a common generatrix; the ratio of the diameter of the single main helix to the diameter of the secondary helix and the ratio of the pitch of the single main helix to the pitch of the secondary helix being identical integers greater than 1.

2. An improvement as defined in claim 1, including two identical secondary helices extending externally of and parallel to said single main helix along diametrically opposed sides thereof, said secondary helices contacting said single main helix at several locations along diametrically opposed generatrices common to said single main helix and to one and the other secondary helix.

3. An improvement as defined in claim 1, wherein the said secondary helix extends over a length shorter than the single main helix.

4. An improvement as defined in claim 2, wherein the said two secondary helices extend over a length shorter than the single main helix.

5. An improvement as defined in claim 1, wherein each said ratio is 2.

6. A microwave electron tube comprising A. a single main helix,

B. an electron gun disposed adjacent oneend of said single main helix in the longitudinal axis thereof to emit an electron beam travelling inside and coaxially with said single main helix,

C. a collector of electrons disposed adjacent the other end of said single main helix in the longitudinal axis thereof to receive the electrons forming said electron beam and D. at least one secondary helix extending externally of and parallel to said single main helix; turns of said single main helix being in direct electric contact with turns of said secondary helix at several locations along coinciding generatrices of said single main helix and second secondary helix; theratio of the diameter of said single main helix to the diameter of said secondary helix and the ratio of the pitch of said single main helix to the pitch of said secondary helix being identical integers greater than 1 7. A microwave electron tube as defined in claim 6, wherein the number of the secondary helices is at least two; said secondary helices are evenly distributed about said single main helix. 

1. In an electron tube delay line for a microwave electronic tube, the improvement comprising A. a single main helix wound cylindrically with an even pitch and adapted to be traversed internally and axially by an electron beam and B. at least one secondary conductor helix wound cylindrically with an even pitch in the same direction as said single main helix and extending externally thereof and parallel thereto; said single main helix and said secondary helix being in electric contact with one another at several locations along a common generatrix; the ratio of the diameter of the single main helix to the diameter of the secondary helix and the ratio of the pitch of the single main helix to the pitch of the secondary helix being identical integers greater than
 1. 2. An improvement as defined in claim 1, including two identical secondary helices extending externally of and parallel to said single main helix along diametrically opposed sides thereof, said secondary helices contacting said single main helix at several locations along diametrically opposed generatrices common to said single main helix and to one and the other secondary helix.
 3. An improvement as defined in claim 1, wherein the said secondary helix extends over a length shorter than the single main helix.
 4. An improvement as defined in claim 2, wherein the said two secondary helices extend over a length shorter than the single main helix.
 5. An improvement as defined in claim 1, wherein each said ratio is
 2. 6. A microwave electron tube comprising A. a single main helix, B. an electron gun disposed adjacent one end of said single main helix in the loNgitudinal axis thereof to emit an electron beam travelling inside and coaxially with said single main helix, C. a collector of electrons disposed adjacent the other end of said single main helix in the longitudinal axis thereof to receive the electrons forming said electron beam and D. at least one secondary helix extending externally of and parallel to said single main helix; turns of said single main helix being in direct electric contact with turns of said secondary helix at several locations along coinciding generatrices of said single main helix and second secondary helix; the ratio of the diameter of said single main helix to the diameter of said secondary helix and the ratio of the pitch of said single main helix to the pitch of said secondary helix being identical integers greater than
 1. 7. A microwave electron tube as defined in claim 6, wherein the number of the secondary helices is at least two; said secondary helices are evenly distributed about said single main helix. 